Effect of density on peeling limited pedestals in JET-ILW, MAST-U and TCV and implications for ITER pedestal predictions

Abstract Plasmas with low collisionality and with the pedestal limited by peeling modes have been achieved in JET-ILW, MAST-U and TCV. The achieved electron–electron pedestal collisionality and the achieved ratio between electron separatrix density to pedestal density are in the ranges ν e ∗ ped = 0.1 − 0.4 and n e sep / n e ped = 0.3 − 0.9 , approaching ITER values. In these conditions, the experimental results show that the pedestal pressure increases with increasing density and no degradation of the pedestal pressure with increasing n e sep / n e ped has been observed. These behaviours are opposite to what observed in ballooning limited pedestals. However, in all three machines, both the increase of the pedestal density and the increase of the separatrix density destabilize the ballooning modes and tend to move the pedestal from being peeling limited to being limited by coupled peeling–ballooning modes. The Europed pedestal predictions have been validated against the experimental results in all the three machines, showing a good qualitative agreement and a reasonable quantitative agreement when approaching ITER-relevant parameters of ν e ∗ ped and ρ ∗ ped (normalized ion Larmor radius). The Europed predictions have been applied to ITER showing that the instabilities that will limit its pedestal strongly depend on the values of and n e sep . Nonetheless, assuming type I ELMy H-modes, the ITER pedestal in the Q = 10 scenario will reach p e ped ≈ 60 kPa